Surface treatment and lens enhancement.pptx

Coating of Lens
Surface treatment for lens

1. Lens enhancement & aberrations of the lens

2. LENS ENHANCEMENT

3. INTRODUCTION: Surface treatment or lens coating improve visual comfort and protect lenses from scratches,dust and reflection.different lens brand offer wide variety of surface treatment that enhance the user’s vision and durability of the lens.it can be applied on either front or back surface of the lens

4. TYPES OF COATINGS : Hard coating Anti-reflection coating Hydrophobic coating Anti-fog coating Mirror coating Anti-static coating UV coating Oleophobic coating Anti-mist coating Blue light preventive coating

5. INDICATIONS OF COATING: Protection from harmful radiations. Better cosmetic appearance. Resisting scratches. Keep your lens away from fogging up. Improving the clarity of the lens. Eliminating unwanted reflections.

6. HARD COATING: Also known as scratch resistant coating plastic lens materials are softer and more prone to scratches than glasses .this coating gives more hardness to plastic lens surface and increases the resistance towards scratches.hard coatings are usually indicated for lenses with a higher refractive index (1.50)

7. CHARACTERISTICS OF HARD COATING: Hard coatings are thin layer about (0.5 to 10 microns)to prevent cracking. Refractive index of the coating should be closely matched to the refractive index the lens material. It may applied on front or back , or both surface of the lens. It reduces surface reflection and increases light transmission. SRC lenses are available in tinted and non tinted form .but, non tinted forms are more scratch resistant.

8. TYPES OF HARD COATINGS: 2 TYPES: 1 THERMALLY CURED HARD COATINGS 2 UV CURED HARD COATINGS

9. THERMALLY CURED HARD COATING : With this hard coating process ,lens are dipped in a varnish and removed from the varnish at a consistent rate to control thickness of the coating. The lenses are then thermally cured or baked over an extended period of time. This method commonly used by lens manufacturers.

10. UV CURED HARD COATING : Scratch resistant coatings can be applied using a system that spins the coating on the lens. It then uses UV light to cure the coating.

11. ADVANTAGES: Increase transmission of light by minimising surface reflections. Protect lens surface from abrasion produced by a sharp object and dust particles DISADVANTAGES: Coating can be damaged by intense heat and chemicals. Poor coated lens produces visual discomforts.

12. HYDROPHOBIC COATING Hydrophobic coating are introduced by Pilkington glass in 2001 The word hydrophobic means water repelling and the hydrophobic coating stops water droplets from sticking on the lens surface The surface keep the lens clean and dust free

13. Characteristics Transparent coating about 20 to 30 nm of titanium oxide or use a filim of silicon with 10 nm thickness The coating acts like a lotus leaf which make spherical droplets of water that slides of easily Dipping process or vacuum methods are used for applying hard coat on the lens surface It usually coated over the anti reflective coating

14. Indications .visual discomfort due to rain, water . Athletes . Wearer with a sweating problem

15. Advantages Increase life of ARC coating Easy to clean Prevent moisture build up Keep dust and dirt particle away from it

16. Disadvantages Chances of slippering during the edging process They won’t protect all types of scratches Poor coating might get damaged.

17. ANTI-REFLECTIVE COATING This coating developed by Alexander smakula in 1935 Anti-reflection coating is also known as reflection free coating or anti-glare coating Thin layer of optical coating applied on lens surface for minimizing reflections and increasing transmission of the lens.

18. Types of reflections The reflecting power of a lens surface is known as catoptrics power. Mainly four troublesome reflection which cause visual disturbance to a spectacle wearer and produce ghost image A false image formed on the image plane due to unwanted reflection is known as a ghost image 1.frontal reflection Occur when some of the light incident on a front surface is reflected towards an observer

19. 2.Backward reflection Occurs when some light behind the patient is reflected from the back surface of lens to his eyes 3. Internal reflection Occur when light is reflected between the two-lens surface 4.Corneal reflection Occur when light is reflected from corneal surface then interacting with the lens surface *by front lens surface *by back lens surface

20. MIRROR COATING A mirror coating can be applied by a vacuum process to the front surface of the lens causing the lens to have the same properties as a two-way mirror When applied as a full-mirror coating the observer is unable to see the wearers eyes and see his or her own image reflected.

21. •Anti fog coating stops lenses from misting up in the humid environment like cooking,sports,activity etc •Fogging of the lens occurs when the lens is significantly cooler than the surroundings •This coating removes the condensation of moisture on lenses by dispersing the water droplet into an invisible thin sheet ANTI-FOGGING COATING

22. CHARACTERISTICS OF ANTI-FOG COATIN G •Anti fog coating are thin layer of hydrophilic material such as titanium dioxide ,polyvinyl alcohol etc •Hydrophilic material absorb water and spread it over the lens surface and prevent condensation of moisture on the lenses . Anti-fog agents are available in the form of spray, wipes or coating.

23. I NDICATION OF ANTI -FOG LENSES • Working in temperature changing environment •Professional who use facial mask likes surgeon, nurse etc •Drivers Swimmers •People who works in altitude and in air condition •indoor activities like boiling water,drinking hot coffee etc

24. Advantage Keep your lenses away from the fogging. Disadvantage Chemicals may damages the coating. Effect of the ant-fog spray does not long last effect.

25. ANTI-STATIC COATING •Anti-static coating play a crucial role in maintaining the clarity and performance of various lenses, including those used in eyeglass ,cameras and other optical devices •This articles explore the science behind anti-static coating,their benefits ,and their application

26. UNDERSTANDING STATIC ELECTRICITY Static electricity is a common phenomenon that occurs when two surface come into contact and exchange electrons This exchange can be in one surface becoming positively charged, while the other becomes negatively charged In the case of lenses , static electricity can attract dust, lint, and other particles compramising visibility and optical quality .

27. THE ROLE OF ANTI STATIC COATING •Anti static coating are designed to mitigate the effect of static electricity on lens surface •These coating typically consist of thin layers applied to the lens that modify its surface properties •The key goal is to create a more neutral charge, making it difficult for static to accumulate and reducing the attraction of particles

28. BENEFITS OF ANTI -STATIC COATING I MPROVED VISIBILITY By minimizing the accumulation of dust and debris ,anti static coating contribute to clearer vision through lenses ,this is particularly crucial for eye glasses wearers who rely on unobstructed vision

29. EXTENDED MAINTENANCE INTERVAL Lens with anti static coating require lens frequent cleaning compared to untreated lenses. This not only save time but also reduce the risk of scratches or damage during cleaning ENHANCED USER EXPERIENCE Anti static coating contribute to a more enjoyable and hassle -free user experience , especially for photographers , outdoor anthusiasts,and individual working in environment prone dust or static

30. APPLICATION IN VARIOUS INDUSTRIES • EYE WEAR Anti static coating are commonly applied to eyeglasses to enhance the wearers comfort and maintain optical clarity •PHOTOGRAPHY Camera lenses benefit from anti static coating to ensure optimal image quality by minimizing the impact of dust and particles during photography

31. • MEDICAL DEVICE Optical equipment used in medical settings such as microscope and endoscope may features anti static coatings to maintain precision and quality • ELECTRONICS Anti static coating can be applied to display screen, ensuring a clearer view and preventing the attraction of dust in electronic devices

32. ULTRA VIOLET COATING •These coating are transparent layers applied to eyeglass lenses to block ultra violet radiation •UV rays, both UVB AND UVA,can contribute to various eye conditions ,and the coating help minimize the potential harm .

33. UV coatings are particularly beneficial in preventing cataract and other eye disorders caused by prolonged exposure to uv radiation When selecting eyeglassess,consider opting for lenses with uv coatings for comprehensive eye care These coatings typically consist of compounds that are transparent to visible light but effective in absorbing harmful uv rays The coatings act as a barrier, preventing a significant Portion of UVA and UVB rays from reaching the eye .

34. •This helps to reduce risk of eye damage associated with uv exposure ,such as cataract and other uv related condition •The composition of ophthalmic lens uv coating can vary, but they commonly include material that effectively absorb or block ultra violet radiation •some of the compound used in these coatings may be organic or inorganic substance with specific properties that make them suitable for uv protection .

35. •organic materials, coatings containing benzotriazole derivatives ,are often employed for their uv absorbing properties •inorganic material like metal oxides can also be used to create a reflective surface that helps block uv rays

36. ADVANTAGES • UV protection The primary advantage is the protection against harmful ultra violet rays ,reducing the risk of eye conditions such as cataract and other uv related disorder •Eye health Uv coating contribute to overall eye health by preventing potential damage caused by prolonged exposure to uv radiation Invisible Protection . The coating is typically transparent, offering uv protection without affecting the appearance of the eyeglass lens.

37. DISADVANTAGE • Cost Eyeglasses with uv coatings may be slightly more expensive than those without adding to the overall cost of eye wear Not complete protection While uv coating provides significant protection ,they may not block 100% of uv rays.some uv light can still reach the eye from the sides or back of the lenses Additional maintenance . Users need to take care when cleaning their coated lenses to avoid damaging the uv coating.

38. ANTI-MIST COATING An anti-mist coating on a lens, whether for eyeglasses or camera lenses, is a thin layer applied to the surface to prevent fogging. This coating typically works by altering the behavior of water droplets that may form on the lens due to temperature and humidity changes. The coating reduces the surface tension of water, causing droplets to spread out and form a thin, transparent layer instead of clumping together into visible fog. This helps maintain clarity and visibility through the lens, even in conditions where fogging would normally occur. Anti-mist coatings are useful for various applications, including eyewear for clear vision and camera lenses to ensure sharp, unobstructed images in challenging environments.

39. OLEOPHOBIC COATING An oleophobic coating on a lens is a thin, protective layer designed to resist oils and fingerprints. This coating repels substances that can adhere to the lens surface, making it easier to clean and maintaining optical clarity over time. It’s commonly used in camera lenses, eyeglasses, and smartphone screens to enhance durability and visibility.

40. BLUE LIGHT PREVENTIVE COATING The bluelight prevention coating on a lens is a specialized layer that aims to reduce the transmission of high-energy blue light. Blue light is emitted by digital screens and artificial lighting, and prolonged exposure can contribute to eye strain and disrupt sleep patterns. This coating helps mitigate these effects by filtering or blocking a portion of the blue light, offering a more comfortable viewing experience and potentially supporting better eye health, especially for individuals who spend significant time on digital devices.

41. In summary, ophthalmic lens coatings serve a multifaceted purpose, addressing issues such as glare, scratches, and exposure to harmful light. As technology advances, these coatings continue to evolve, contributing to improved eye health and an enhanced visual experience for individuals relying on corrective lenses.

42. Aberrations of lens

43. CHROMATIC ABERRATION: In  optics ,  chromatic aberration  ( CA ), also called  chromatic distortion  and  spherochromatism , is a failure of a  lens  to  focus  all  colors  to the same point. It is caused by  dispersion the refractive index  of the lens elements varies with the  wavelength  of  light . The refractive index of most transparent materials decreases with increasing wavelength.Since the  focal length  of a lens depends on the refractive index, this variation in refractive index affects focusing.Chromatic  aberration manifests itself as "fringes" of color along boundaries that separate dark and bright parts of the image.

44. SPHERICAL ABERRATION: Spherical aberration is a Seidel aberration that occurs when parallel light from an object enters a large area of a spherical lens surface. When spherical aberration is present ,peripheral rays focus at different points on the optic axis than do paraxial rays, Ie,(peripheral rays are those that enters the lens nearer the edge than the centre.paraxial rays are those that pass through the central area of the lens) Spherical aberration occurs when the object point is on the optical axis of the system.

45. CURVATURE OF FIELD: Curvature of field means, A defect in an optical system that results in points on an object plane perpendicular to the axis being imaged on a curved surface rather than on a plane. The aberration curvature of field occurs when the light entering the peripheral areas of the lens does not focus where it should, namely on the far point sphere. (the far point sphere is curved because the eye turns to see objects towards the periphery of lens) Instead it focus on the petzval surface (image surface) it is formed when oblique astigmatism is corrected.

46. It is important to use manufacturer’s recommended use curve for each given lens power The optimum base curve will ensure that oblique astigmatism and power error are held to a minimum. When using wrong base curve, the wearer will not be able to see as well through the periphery of the lens.

47. Coma aberration The effect of Rays from an object point not situated on the axis of lens results in an aberration called coma. Comatic aberration is similar to spherical aberration in that both are due to failure of lens to bring all rays from a point object to focus at the same point. Spherical aberration refers to object points situated on the axis whereas comatic aberration refers to object points situated off the axis. In the case of spherical aberration, the image is circle of varying diameter along the axis and in the case of comatic aberration the image is comet-shaped and hence the name coma.

48. In this figure the presence of coma in the image due to point object O, situated of the axis of the lens. Rays of light getting refracted through the centre of the lens (ray 1) meet the screen XY at the point P. Rays 2,2;3,3 etc getting refracted through the outer zones of the lens come to focus at points Q,R,S, etc, nearer the lens and overlapping circular patches of gradually increasing diameter are formed on the screen. The resultant image of the point is comet-shaped as indicated on the right side of the figure.

49. Coma is the result of varying magnification for rays refracted through different zones of the lens. In the above, rays of light getting refracted through the outer zones come to focus at points nearer the lens. Hence, the magnification of the image due to the outer zones is larger than the inner zones and in this case coma is said to be positive. On the other hand if the magnification produced in an image due to the outer zones is smaller, coma is said to be negative. Applanatic lens : A spherical lens , which is free from the defect of spherical aberration and coma.

50. Astigmatism Astigmatism, similar to coma , is the aberration in the image formed by a lens , of object points off the axis . The difference between astigmatism and coma , however, is that in coma the spreading of the image take place in a plane perpendicular to the lens axis and in astigmatism the spreading takes place along the lens axis . Astigmatism discussed in this article is different from the one treated in defective vision.

51. In this figure the defect of astigmatism in the image of a point B situated off the axis. Two portions of the cone of rays of light diverging from the point B are taken. The come of the rays of light refracted through the tangential (vertical) plane BMN comes to focus at point P1 nearer the lens and the cone of rays refracted through the sagittal (horizontal) plane BRS comes to focus at the point P2 away from the lens. All rays pass through a horizontal line passing through P1 called the primary image and also through a vertical line passing through P2 called the secondary image.

52. Distortion The failure of the lens to form a point image due to a point object is due to the presence of spherical aberration,coma and astigmatism. The variation in the magnification produced by lens for different axial distances results in an aberration called distortion.

53. This aberration is not due to the lack of sharpness in the ‘image’. Distortion is of two types. A) pin-cushion distortion and B) berrel-distortion . In pin-cushion , the magnification increases with increasing axial distance and the image of an object. On the other hand, if the magnification decreases with increasing axial distance, it results in barrel-shaped distortion.

54. In the absence of the stop which limit come of rays or light striking the lens, a single lens is free from distortion. But, if stops are used the resulting image is distorted. If a stop is placed before the lens the distortion is barrel-shaped [fig (a)]. If the stop is placed after the lens , the distortion is pin-cushion type [fig(b)]. To eliminate distortion is placed in between two symmetrical lenses, so the pin-cushion distortion produced by the first lens is compensated by the barrel-shaped distortion produced by the second lens.

55. By Group - 4